A new generation of optoelectronic devices such as organic photovoltaic (OPV) devices, organic light emitting transistors (OLETs), organic light emitting diodes (OLEDs), organic thin film transistors (OTFTs), printable circuits, electrochemical capacitors, and sensors are built upon organic semiconductors as their active components. To enable high device efficiencies such as large charge carrier mobilities (μ) needed for transistor/circuit operations, or efficient exciton formation/splitting that is necessary for OLED/OPV operations, it is desirable that both p-type and n-type organic semiconductor materials are available. Furthermore, these organic semiconductor-based devices should exhibit satisfactory stability in ambient conditions and should be processable in a cost-effective manner. For example, a benchmark polymer, regioregular poly(3-hexylthiophene) (rr-P3HT), can provide hole mobilities in the order of about 0.1 cm2/Vs and current modulation in the order of about 105 or greater, which is close to amorphous silicon. For OPV devices based on rr-P3HT, power conversion efficiencies (PCEs) as high as about 4% have been reported. However, such performances are not sufficient for commercial applications. Besides, these optimal performances were achieved only under strict device processing conditions.
Bulk heterojunction (BHJ) solar cells commonly are considered the most promising OPV structures because they can be fabricated using roll-to-roll and large-scale production. BHJ solar cells include a photoactive layer disposed between an anode and a cathode, where the photoactive layer is composed of a blend film including a donor material and an acceptor material. State-of-the-art BHJ solar cells use fullerene-based compounds as the acceptor material. Typical fullerenes include C60 or C70 “bucky ball” compounds functionalized with solubilizing side chains such as [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) or [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM). The most common donor material used in BHJ solar cells is poly(3-hexylthiophene) (P3HT). However, it is well known that P3HT-based cells have limited efficiency due to poor light absorption above 500 nm. Furthermore, P3HT has poor air stability.
Accordingly, the art desires new organic semiconducting compounds that can be used as active materials in various optoelectronic devices.